The present invention relates to printers, and more particularly, to a method and apparatus for adjusting the anti-rotation rail in a printer to thereby adjust the printhead-carrying carriage relative to the platen in a printer which correspondingly adjusts the printhead-to-platen spacing.
Inkjet printers typically include a carriage which holds printheads for ejecting ink onto media as the carriage reciprocates along a guide shaft above a platen. The platen provides a surface along which media, such as single-sheet paper or envelopes, are carried.
Conventional inkjet printers include a bearing rail, called an xe2x80x9canti-rotation rail,xe2x80x9d which is mounted on a hanger in the printer, along which an arm of the carriage slides, as the carriage reciprocates along the guide shaft during a printing operation. The anti-rotation rail can be adjusted and fixed, to pivot the carriage, and correspondingly the printhead, relative to the guide shaft, which in turn sets the printhead-to-platen spacing. In the manufacture of printers, it is desirable to pre-set and fix the printhead-to-platen spacing to some nominal distance to ensure optimum print quality. A common practice is to use a measurement tool, such as a linear variable differential transducer (LVDT), by inserting it into the receptacle on a carriage which carries a printhead.
The tool includes a probe which extends downwardly and engages the platen, and a readout informs production or line personnel of the printhead-to-platen spacing. The practice heretofore has been to adjust the anti-rotation rail, which then adjusts the carriage and the printhead-to-platen spacing, to fix that spacing at some nominal amount, say 1.4 mm. This adjusting step is done with a pair of screws mounted on the anti-rotation rail, positioning of these screws being necessary to adjust the anti-rotation rail to a predetermined setting. The next step requires that additional screws, not part of the adjusting process, be used to fix the anti-rotation rail to the hanger. This method has several drawbacks, the first being that line personnel have difficulty keeping track of the multiple screws which can be misplaced. Importantly, a problem resides in the fixing of the anti-rotation rail, after adjustment, because the fixing or tightening can vary an adjustment which has just been made. Thus, the nominal spacing, as a printer unit leaves, may not be achieved. If screws are not properly affixed, vibration during shipping and handling can vary the printhead-to-platen spacing.
The present invention provides apparatus for adjusting and maintaining printhead-to-platen spacing in a printer, and a method for achieving the adjustment which contemplates that the anti-rotation rail is first clamped or fixed to the hanger, followed by the adjusting step where the nominal printhead-to-platen spacing is set. This is accomplished by using a combination clamp structure/adjuster mechanism in which the anti-rotation rail is first clamped to the hanger, and the adjuster mechanism, which includes a rotatable member, is operable for selectively shifting the anti-rotation rail vertically upwardly or downwardly to position and maintain the carriage, and correspondingly, the printhead at a preselected distance from the platen.
The clamp structure typically includes a pin member, such as a screw, which extends through the anti-rotation rail and engages a rotatable member operable for rotation to urge the pin member against the anti-rotation rail to shift the rail to a desired position. In the depicted embodiment, there are two clamp structure/adjuster mechanisms provided, one adjacent each end of the anti-rotation rail. The lateral spacing of the mechanisms ensures that during a production process, line personnel may efficiently and accurately pre-set nominal printhead-to-platen spacing at opposed ends of the carriage travel, thereby ensuring that any offset in the platen will be taken into account.